A gear motor assembly, such as a window lift drive used in a vehicle to raise or lower a window, typically includes a bidirectional motor and a gearbox. The gearbox includes a casing and a gear train in the form of a worm and worm gear disposed in the casing. The motor includes a stator and a rotor. The stator includes a housing and permanent magnets attached to an inner surface of the housing. The rotor is rotatably disposed in the stator. The rotor includes a motor shaft, a core and a commutator fixed to the shaft. The shaft extends into the gearbox casing and has a worm which is meshed with the worm gear to rotate the worm gear, and thus a load attached to the worm gear. Two axial ends of the motor shaft are respectively spaced from either of the motor housing or the gear casing. When the motor changes the direction of rotation, axial vibrations of the motor shaft are created, which may damage the worm gear.
Therefore, there is a desire for an improved gear motor assembly in which end play is eliminated or closely controlled to avoid damage to the worm gear due to axial vibrations of the motor shaft.